Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already mark it read-only/non-destructive, and the description adds genuinely new behavioral facts: 400 on malformed address, 404 on address without code, both uncharged, and that every successful call is billed so repeats are not free — which explains the idempotentHint=false. Pricing (x402 USDC, card key, first 25 free) and the 'reads or computes only and changes nothing' guarantee round out the contract with the caller.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with purpose and standards, then usage, then error/pricing semantics in descending importance — no sentence is filler. The billing tail is somewhat dense and could be split, but each clause carries usable information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Complete for a one-parameter read tool: it covers what is resolved, when to use it, error outcomes and cost. What is under-specified is the shape of the result — which of implementation/beacon/admin addresses come back and in what form — though with no output schema and a simple return, this is a minor gap.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The single parameter is fully documented in the schema (100% coverage), so the baseline is 3; the description adds value with a concrete worked example address (0x3c49…3359) and an explicit validation rule (malformed address → 400). It does not describe address formatting constraints beyond the example.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Find the implementation behind a proxy contract on Polygon PoS') and enumerates exactly which standards it resolves (EIP-1967 impl/beacon/admin slots, EIP-1822/UUPS, legacy OZ layout, EIP-1167 minimal proxy) plus that it names the proxy kind. This is far more specific than the sibling chain-family names (eth_proxy, arb_proxy, base_proxy) and lets an agent pick correctly.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives a clear trigger ('use before trusting or decoding a contract whose code can be swapped by its admin') and names the escalation path ('for a fuller risk verdict use contract_risk'). It stops short of an explicit when-not (e.g. for non-proxy or EOA addresses, or how it differs from polygon_storage/polygon_is_contract), so it falls just below the top band.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.